1. Field of the Invention
This invention relates to timing devices. Particularly, the invention relates to a timer having a metered orifice through which a solid particulate medium flows for measurement of a time interval.
2. Description of the Prior Art
Hour glasses and timing devices which employ a quantity of a flowing, solid particulate medium have been known for centuries. Typically, these timers are constructed to have a particulate medium flow from a first chamber, through a metered orifice and into a second chamber. Once all of the particulate medium flows into the second chamber, the measurement of a time interval has been completed.
The particulate medium employed by such timers is pulled through the metered orifice from one chamber to the other because of the influence of gravity. The rates of flow within such timers are determined jointly by the size of the orifice between the chambers and by the nature of the particulate medium employed.
When the measurement of a time interval has been completed, most timers of this sort are typically inverted to start the flow of the particulate medium in the opposite direction. For the measurement of a second time interval, the particulate medium flows from the second chamber, through the metered orifice and back into the first chamber.
A difficulty with timers of this sort is that the particular time interval must be completed before restarting another by inversion. For an accurate measurement of a subsequent time interval, all of the particulate medium must flow through the metered orifice and into one of the aforementioned chambers. There is no easy way to quickly reset these timers.
It is known in the art that the metered orifice to such timers can be modified with moving parts for minimizing time loss due to resetting. For example, in U.S. Pat. No. 3,125,849, the timer was provided with a valved orifice which could be rotatably switched to one of several positions. In a first position, the particulate medium could flow from a first chamber through the timing orifice and into a second chamber for measurement of a time interval. In a second position, the setting position, the particulate medium could flow through a larger orifice at a more rapid pace. Because of quicker flow through this second orifice, less time was lost to resetting of the timer. Lastly, in a third position, the two chambers of this timer were completely separated to stop the flow of the particulate medium therebetween.
In a second, rapidly resettable timer, the two chambers were separated by a cup-shaped valve having a metered orifice or vent in the middle of one end. Exemplary of such a device is U.S. Pat. No. 2,144,857. The valve was attached to the base of one of the two chambers by a movable valve seat. When the valve was in its first position with the timer righted, a flowing medium passed through the vent and into a lower chamber for the measurement of a timing interval. When this timer was )inverted, the valve was pulled downward by gravity to open two (2) return passages for the flow of the particulate medium back to the original chamber.
Both of the aforementioned timers required some sort of moving part. Additionally, both devices required that the particulate medium flow through at least one and preferably two orifices for resetting. Though the sizes of these orifices were larger than their respective metered orifices, time was still lost to the flow of the particulate medium through these passageways during the reset stage for each timer.
In U.S. Pat. No. 4,408,894, a resettable timer was disclosed which did not employ some sort of moving part. The timer therein was resettable for selected time intervals depending upon the amount of particulate medium that was loaded into a measuring chamber. However, the resetting or loading of this timer required rotation of the device in a specific, selected direction. The only way to load the particulate medium was by a clockwise rotation of this timer.